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    <title>案例1</title>
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<h1>登岳阳楼</h1>
<h5>唐代：杜甫</h5>
<p>昔闻洞庭水，今上岳阳楼。</p>
<p>吴楚东南坼，乾坤日夜浮。</p>
<p>亲朋无一字，老病有孤舟。</p>
<p>戎马关山北，凭轩涕泗流。</p>
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    //这里的document.querySelector("h5")是获取到一个以h5标签的dom对象，
    dom = document.querySelector("h1");
    //修改该对象的style属性的color的值
    dom.style.color='red'
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